Fatigue-damage analysis under various loading conditions

Abstract

A fatigue-damage parameter for in-phase and out-of-phase loading is proposed. A proposed fatigue-damage parameter has been developed to assess the various materials fatigue lives for (i) constant-amplitude fatigue stressing where the stresses are at the same and different frequencies, and (ii) variable-amplitude loading conditions. In this parameter, the normal and shear stress and strain ranges have been calculated from the largest stress and strain Mohr’s circles. The total damage accumulation in a block-loading history has been calculated from the summation of the normal and shear energies on the basis of a cycle-by-cycle analysis. The normal and shear energies used in this parameter are divided by the tensile and shear-fatigue properties, respectively, and the proposed parameter, unlike many other parameters, does not use an empirical fitting factor. The proposed parameter successfully correlates fatigue lives of several materials for: a) various in-phase and out-of phase fatigue-loading conditions, b) tests in which a mean stress was applied normal to the maximum shear plane, and c) out-ofphase tests in which there was additional hardening.